A compressor employed in an automotive cooling system for cooling the driver's compartment of a vehicle is required to operate under varying speed conditions and with a large delivery capacity while the system is working to decrease the compartment temperature. When a comfortable temperature has been reached in the compartment and, therefore, the system only has to maintain that level of temperature, the compressor is not required to operate under such a large delivery capacity as before, and it is desirable that the compressor be switched to a partial-load operation. Moreover, the compressor must be capable of such partial-load operation under the same varying speeds of auto engine operation.
Accordingly, an object of the present invention is to provide a rotary compressor which can be operated, when required, under a partial load by reducing its delivery capacity substantially in the entire range of operating speeds.